1. Field of the Invention
This invention relates to the preparation of tetraalkoxysilanes by the direct reaction of alkanol with silicon.
2. Description of the Prior Art
The most common route of tetraorganooxysilanes is the reaction of silicon tetrahalides with alcohols or their salts. The esters can also be made by transesterification, by reaction of alcohols with SiO.sub.2, SiS.sub.2, hydridosilanes, or silicon alloys such as Mg.sub.2 Si or Ca.sub.2 Si.sub.2, and by direct reaction of alcohols with silicon.
One such direct reaction involves the formation of alkoxysilanes from alcohols and silicon, ferrosilicon, or iron silicide in the presence of metal alkoxide catalysts. Ethoxysilanes have also been formed by the electrolysis of ethanol with silicon-containing anodes and by the reaction of ethanol with hyperactive silicon formed from calcium silicide and chlorine. Further, silicon can be reacted with alcohols in the presence of copper or copper halides when suspended in liquid such as polycyclic aromatic hydrocarbons or silicone oils. Likewise, copper-catalyzed reactions of silicon with alcohols in the gas phase are known.
U.S. Pat. No. 2,927,937 discloses the use of alkaline catalysts such as ammonia in the direct reaction of ethanol with silicon. U.S. Pat. No. 3,505,379, in column 7, lines 31-36, teaches that tetraethylorthosilicate formation from Si and C.sub.2 H.sub.5 OH is possible if the reaction be carried out in the presence of basic substances. However this patent teaches, loc cit, that such tetraethylorthsilicate formation should be avoided, presumably because the object of the patented invention is the production of organosilanes. Such prior art generically teaches the equivalence of "alkaline catalyst" and "basic substances" in the reaction in question. Thus, not only does such prior art fail to recognize the importance of employing copper-activated silicon in the reaction, but also it fails to recognize the advantages of utilizing dimethylamine therein.